1. Field of the Invention
The present invention relates to a thin-film magnetic head for perpendicular magnetic recording used for recording information on a recording medium by means of a perpendicular magnetic recording method.
2. Description of the Related Art
In recent years, the surface recording density of a magnetic disk device has been remarkably improved. In particular recently, the surface recording density of a magnetic disk device has reached 160 to 200 gigabytes/platter, and furthermore is so vigorous as to exceed such a recording density. With this, the improvement in performance of a thin-film magnetic head is demanded.
Thin-film magnetic heads can be classified roughly into a magnetic head of a longitudinal recording method for recording information in a longitudinal direction in the recording surface of a magnetic disk and a magnetic head of a perpendicular recording method for recording information in the perpendicular direction to the recording surface of it according to their recording methods. Between them, a thin-film magnetic head of a perpendicular recording method is conceived to be more hopeful than that of a longitudinal recording method since a thin-film magnetic head of the perpendicular recording method can realize much higher recording density in comparison with a thin-film magnetic head of the longitudinal recording method and moreover a recorded magnetic disk of the perpendicular recording method is more difficult to suffer from the influence of thermal fluctuation. A thin-film magnetic head of a conventional perpendicular recording method has been disclosed for example in U.S. Pat. No. 6,504,675 Specification, U.S. Pat. No. 4,656,546 Specification, U.S. Pat. No. 4,672,493 Specification, and Japanese Patent Laid Open Publication No. 2004-94,997 and the like.
By the way, in a thin-film magnetic head of a perpendicular recording method, when data are recorded on an inner or outer circumferential region of a magnetic disk, a magnetic pole end portion located at the medium facing surface (referred to as an air bearing surface or ABS also) facing the magnetic disk has a skew angle of a certain angle to a track to have data recorded on it.
In case of a perpendicular magnetic recording head having a high writing ability, there may occur a problem called a writing blur resulting in recording extra data between adjacent tracks due to such a skew angle. The occurrence of such a writing blur has a harmful influence on the detection of a servo signal or the S/N ratio of reproduced waveform. Thereupon, in a conventional perpendicular magnetic recording (PMR) head, a magnetic pole end portion at the ABS side in a main magnetic pole film is made into a bevel shape becoming gradually narrower in one direction (see Japanese Patent Laid Open Publication No. 2003-242,607 and Japanese Patent Laid Open Publication No. 2003-203,311).
As a PMR head having a magnetic pole end portion of a bevel shape, there is known a PMR head provided with a lower yoke layer, a main magnetic pole film having a bevel-shaped magnetic pole end portion, and a write shield layer facing the main pole film with a recording gap film between them at the ABS side. A PMR head of this type is also demanded to be narrower in track width in order to improve the recording density. Furthermore it is desirable to be good in overwrite characteristic and prevent other data from being overwritten on data recorded on a magnetic disk. For this, it is desirable to make a structure in which the lower yoke film is as close to the ABS as possible.
In a PMR head of this type, however, since a main magnetic pole film is formed next to the lower yoke film, a neck height is generated by the influence received by the lower yoke film when the main magnetic pole film having a bevel-shaped magnetic pole end portion is formed, and thereby a narrow part corresponding to a track width is lengthened by the neck height portion and as a result there has been the possibility of shifting from a designed length.
Since the lower yoke film has to be formed distantly from the ABS in order to avoid the influence of such shifting of neck height, it has been difficult to make large the quantity of magnetism (called magnetic volume also) in a location close to the ABS. Therefore, in a conventional PMR head there has been a problem that it is difficult to have a good overwrite characteristic.